Method and apparatus for operating an electric water heater

ABSTRACT

A control system for an electric water heater having an upper heating element and a lower heating element is disclosed. The control system includes a control module that controls operation of the electric water heater by selectively toggling the upper and lower heating elements between an ON state and an OFF state and a consumer interface module that allows a consumer to input a set point temperature and select an energy savings mode for the electric water heater. The control module regularly monitors hot water usage and adjusts the set point temperature by a predetermined setback amount until a capacity of the water heater matches consumer usage.

FIELD OF THE INVENTION

The present invention relates to electric water heaters and moreparticularly to a control system for controlling the capacity of anelectric water heater for energy efficiency.

BACKGROUND OF THE INVENTION

Electric water heaters are conventionally used in residential andcommercial buildings to supply the occupants of the building with areservoir of hot water. The water heater typically includes a tank thatis fluidly coupled to a water supply of the building at an inlet and isfluidly coupled to building fixtures such as faucets, showers, anddishwashers at an outlet. The water heater tank receives cold water fromthe building water supply at the inlet and heats the water to a setpoint temperature using lower and upper heating elements. The lower andupper heating elements raise the temperature of the water disposedwithin the water heater tank to the set point temperature by convertingcurrent from a building power supply into radiant heat. The heated wateris stored within the tank and is held at the set point temperature bythe heating elements so that a supply of hot water is constantly andconsistently provided at a desired temperature.

Conventional electric water heaters typically include a control systemthat monitors a temperature of water disposed within the water tank toensure that the water contained therein is maintained at a predeterminedset point temperature. The set point temperature is typically aconsumer-selected setting that allows the consumer to determine atemperature of the hot water to be produced by the water heater. Thecontrol system continuously monitors the temperature of the water withinthe tank via a temperature sensor and compares the sensed temperature tothe set point temperature. The control system generally includes anupper temperature sensor associated with the upper heating element and alower temperature sensor associated with the lower heating element. Theupper temperature sensor and lower temperature sensor each provideinformation regarding the water temperature near the respectiveelements. The respective sensors, in combination with the upper andlower heating elements, allow the control system to selectively heat thewater disposed within the tank when the sensed temperature falls belowthe set point temperature.

In operation, the upper heating element of a conventional electric waterheater is energized by the control system to heat a volume of watergenerally between the upper heating element and a top of the tank (i.e.,an upper zone of the tank). Once the water in the upper zone of the tankis at the set point temperature, the control system de-energizes theupper heating element and energizes the lower heating element. The lowerheating element heats a volume of water generally above the lowerheating element and below the upper heating element (i.e., a lower zoneof the tank). The lower heating element remains energized until thewater within the lower zone of the tank is at the set point temperature.

Water, when heated, rises due to the physical properties (i.e., density)of heated water relative to the cooler water within the tank. Therefore,as the lower heating element heats water, the heated water rises withinthe tank and cold water descends toward the lower heating element. Thedescending cold water mixes with the passing hot water and is heated bythe lower heating element. This process continues until the entirevolume of water disposed within the lower zone of the tank reaches theset point temperature.

When a consumer draws hot water from the tank, the initial hot waterdrawn from the tank outlet is disposed within the top zone of the tank,near the upper heating element and upper temperature sensor. When thehot water exits the tank, a fresh supply of cold water is introducedinto the tank at an inlet. The inlet is generally disposed at a bottomof the tank, below the lower heating element. The incoming cold watereventually contacts the lower heating element as the hot water isdisplaced (i.e., drawn from the tank at the outlet). At this point, thelower temperature sensor detects the influx of cold water and relays theinformation to the control system. The control system processes theinformation from the lower temperature sensor and energizes the lowerheating element to heat the incoming cold water until the set pointtemperature is achieved.

If the consumer does not use all of the hot water available in the tank,the lower heating element remains energized and continues to heat thewater (as described above) until the set point temperature is reached.However, there are instances when the consumer draws a sufficient volumeof hot water from the tank such that the volume of cold water enteringthe tank reaches the upper heating element. Such an occurrence is knownas a “deep draw” event. A deep draw event is identified when the uppertemperature sensor detects a significant drop in temperature due to theincoming cold water. Upon detection of the incoming cold water, thecontrol system de-energizes the lower heating element and energizes theupper heating element in an effort to quickly heat the smaller volume ofcold water above the upper element to the set point temperature beforethe water exits the tank.

When the consumer stops using hot water, the influx of cold water issimilarly stopped. At this point, the upper heating element continues toheat water disposed in the upper zone of the tank until the uppertemperature sensor detects that the water disposed in the upper zone isat the set point temperature. The control system then de-energizes theupper heating element and energizes the lower heating element to heatthe water disposed within the lower zone of the tank. The lower heatingelement remains energized until the lower temperature sensor detectsthat the temperature of the water disposed within the lower zone is atthe set point temperature. In this manner, conventional hot waterheaters include a control system that responds to a draw of hot waterfrom the tank by continually heating the entire volume of water disposedwithin the tank to the set point temperature.

The capacity of an electric water heater is conventionally understood asthe volume of water that the water heater is able to heat and maintainat a set point temperature. For example, an eighty-gallon water heatercan heat and store eighty gallons of water. In this regard, then, thecapacity of the eighty-gallon water heater is eighty gallons.

The effective capacity of the water heater that is realized by aconsumer, however, is greater than the simple volume capacity of thewater heater that was just described. This is so because a consumer doesnot typically use water at the set point temperature when a call for“hot water” at a household fixture is made. While the set pointtemperature for a water heater can vary, it is not uncommon that the setpoint is at 120° F. or higher. A consumer demand for “hot water” at afixture, however, generally is for water at a comfortable temperaturethat is well below the set point temperature. Consequently, in order toproduce the “hot water” that is used by the consumer, water drawn fromthe water heater is mixed with cold water from the building watersupply. Thus, for example, for every gallon of “hot water” that is usedby the consumer, only a half-gallon of water is drawn from the waterheater. This effectively increases the amount of “hot water” that theelectric water heater can provide to a consumer.

As a general proposition, the higher the set point temperature of thewater heater, the lower the volume of water that needs to be drawn fromthe water heater in order to produce “hot water” for the consumer.Similarly, the lower the set point temperature of the water heater, thehigher the volume of water that needs to be drawn from the water heaterin order to produce “hot water” for the consumer. Thus, the effectivecapacity of the water heater can be adjusted by raising or lowering theset point temperature of the water heater. For example, a lower setpoint temperature would require more water from the water heater toproduce the desired “hot water.” Thus, hot water from the water heateris used faster and the effective capacity of the system is reduced.Conversely, raising the set point temperature would require less waterfrom the water heater to provide the same “hot water.” Increasing theset point temperature, therefore, increases the capacity of the waterheater.

A conventional control system for an electric water heater generallyoperates to maintain the entire volume of water in the tank at the setpoint temperature, as described above. These control systems operateindependent of the actual demands for hot water made by the consumer.Therefore, even if the consumer's requirements for “hot water” wereregularly smaller than the effective capacity of the water heater, thewater heater would nonetheless repeatedly heat all of the water to theset point temperature all of the time.

Therefore, it is desirable to provide a control system that cancontinuously monitor and adjust the effective capacity of an electricwater heater based on consumer demands in order to save energyassociated with operation of the electric water heater. Furthermore, itis also desirable to provide a control system that enables the electricwater heater to satisfy government energy standards, whilesimultaneously providing a consumer with an adequate “hot water”capacity.

SUMMARY OF THE INVENTION

Accordingly, a method and apparatus for operating an electric waterheater is provided. The invention comprises a control system including acontrol module and a consumer interface module. The control modulecontrols operation of the electric water heater by selectivelyenergizing and/or de-energizing one or more heating elements. Theconsumer interface module enables a user to input a set pointtemperature for the electric water heater and select an energy savingsmode. The control module continuously monitors and adjusts theuser-selected set point temperature until a capacity of the water heatermatches consumer usage.

Further areas of applicability of the present invention will becomeapparent from the detailed description provided hereinafter. It shouldbe understood that the detailed description and specific examples, whileindicating the preferred embodiment of the invention, are intended forpurposes of illustration only and are not intended to limit the scope ofthe invention.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will become more fully understood from thedetailed description and the accompanying drawings, wherein:

FIG. 1 is a schematic representation of an electric water heater that isoperated in accordance with the principles of the present invention;

FIG. 2 is a schematic representation of a consumer interface module ofthe electric water heater of FIG. 1;

FIG. 3A is a schematic representation of a control module incorporatingan electronic upper limit sensor for an electric water heater inaccordance with the principles of the present invention;

FIG. 3B is a schematic representation of a control module incorporatinga bimetal upper limit switch and electronic upper limit sensor for anelectric water heat in accordance with the principles of the presentinvention;

FIG. 4 is a flowchart that describes the operation of an energy savermodule for an electric water heater in accordance with the principles ofthe present invention;

FIG. 5 is a flowchart that describes the operation of an electric waterheater in accordance with the principles of the present invention;

FIG. 6 is a flowchart that illustrates operation of a consumer interfacemodule for an electric water heater controller in accordance with theprinciples of the present invention;

FIG. 7 is a flowchart that describes the operation of a watertemperature differential module in accordance with the principles of theinvention; and

FIG. 8 is a schematic representation of a control system for a hot waterheater according to the invention and incorporating a sensor module, acontrol algorithm, and a control module.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The following description of the preferred embodiment(s) is merelyexemplary in nature and is in no way intended to limit the invention,its application, or uses.

With reference to the figures, an electric water heater 10 is providedand includes a control module 12. The control module 12 adjusts aneffective capacity of the electric water heater 10 by continuouslymonitoring and adjusting a set point temperature of the water heater 10until an optimum effective capacity of the electric water heater 10 isachieved. As used herein, the term module refers to an applicationspecific integrated circuit (ASIC), an electronic circuit, a processor(shared, dedicated, or group), and memory that execute one or moresoftware or firmware programs, a combinational logic circuit, and/orother suitable components that provide the described functionality.

The set point temperature is a consumer-selected input and is generallydefined as the maximum temperature that the consumer selects for theheated water that exits the water heater 10. The effective capacity ofthe water heater 10 is generally defined as the ability of the waterheater 10 to provide a volume of water at a “delivered temperature.” Thedelivered temperature is the temperature of the water as used by theconsumer at a fixture. The delivered temperature of the water isgenerally lower than the set point temperature because the deliveredtemperature is usually achieved by mixing water from the water heater 10at the set point temperature with cold water from the building watersupply.

The effective capacity of the water heater 10 is directly related to theset point temperature as follows: the higher the set point temperature,the lower the volume of hot water that is necessary to be mixed with thecold water to produce the water at the fixture at the deliveredtemperature. Conversely, the lower the set point temperature, the higherthe volume of hot water that is necessary to be mixed with the coldwater to produce the water at the fixture at the delivered temperature.Therefore, there is a direct correlation between the set pointtemperature and the effective capacity of the water heater 10.

The control module 12 monitors and controls the effective capacity ofthe water heater 10 by selectively adjusting the consumer-selected setpoint temperature. In so doing, the control module varies the effectivecapacity of the water heater 10 to meet the specific needs of theconsumer. By adjusting the effective capacity of the water heater 10 tomeet the demand of the consumer, the control module 12 is able tominimize energy consumption of the water heater 10 while maintaining theability to produce a satisfactory volume of hot water for the consumer.

With reference to FIG. 1, the electric water heater 10 is shown toinclude a tank 14, an upper heating element 16, and a lower heatingelement 18. The tank 14 defines an interior 11 having a volume andincludes an inlet 20 and an outlet 22, both fluidly coupled to theinterior 11. The inlet 20 is also fluidly coupled to a water supply 24,while the outlet 22 is also fluidly connected to the hot water pipesleading to the building fixtures, such as faucets, showers, dishwashers,and clothes washers, etc., which are schematically represented at 26.The inlet 20 receives a constant supply of cold water under pressurefrom the building water supply 24 such that the interior 11 of the tank14 is always full of water. Hot water only exits the tank 14 through theoutlet 22 when a demand for hot water is made at one of the fixtures 26throughout the building. Cold water, therefore, only enters the tank 14when hot water exits the tank 14 through the outlet 22.

The upper heating element 16 and the lower heating element 18 eachextend through a side wall 25 of the tank 14 and generally into theinterior 11. The upper heating element 16 is disposed near an upper wall32 of the tank 14. The lower heating element 16 is disposed near a lowerwall 34 of the tank 14. The lower heating element 18 is generally closerto the lower wall 34 of the tank 14 than the upper heating element 16 isto the upper wall 32.

The upper and lower heating elements 16, 18 receive current from a powersupply 30 via the control module 12. The control module 12 regulateseach of the upper and lower heating elements 16, 18 between an ON stateand an OFF state.

The electric water heater 10 also includes a sensor module 35 (see, FIG.8) in communication with the control module 12. The sensor module 35comprises an upper temperature sensor 36 and a lower temperature sensor38, each in communication with the control module 12. Outputs from theupper and lower temperature sensors 36, 38 which correspond to theirrespective temperature readings are monitored by the control module 12.

The upper temperature sensor 36 is disposed adjacent to the upperheating element 16 to monitor a temperature of water within the tank 14in an upper zone (i.e., generally between the upper heating element 16and the upper wall 32). The lower temperature sensor 38 is disposedadjacent to the lower heating element 18 to monitor a temperature ofwater within the tank 14 in a middle zone (i.e., generally between thelower heating element 18 and the upper heating element 16). Thetemperature sensors 36, 38 are preferably thermistors, such as NTCthermistors, but could be any suitable temperature sensor that canaccurately and reliably provide an output which is indicative of thetemperature of the water residing within the tank 14 near the sensor.

In addition to the foregoing, the sensor module 35 could also comprisetwo or more upper temperature sensors 36 disposed near the upper heatingelement 16. Such an arrangement would provide redundant temperaturereadings at the upper heating element 16. In a device having such anarrangement, the control module 12 would monitor the output from theplurality of sensors 36 and the sensor output indicative of the highestmeasured temperature would be used to control the operation of the upperheating element 16. In addition, the control module 12 can compare therespective outputs from the sensors 36 for a self-diagnostic procedure.For example, if the difference between the output of any two sensors 36is above a predetermined threshold value, the control module 12 coulddetect a sensor fault and require that the water heater 10 be shut downfor maintenance or repair.

Further, the sensor module 35 could also include a flow sensor 37disposed at the inlet 20 or the outlet 22 of the tank 14. The flowsensor 37 could monitor a flow of water entering or exiting the tank 14.Therefore, output from the flow sensor 37 could be used by the controlmodule 12 to control the operation of the upper and lower heatingelements 16, 18. The flow sensor 37 could also be used to determine thevolume of water that has been drawn from the water heater 10 over aperiod of time.

Referring now to FIG. 2, the control module 12 includes a consumerinterface module 45 having a liquid crystal display (LCD) 40, a seriesof light-emitting devices (LEDs) 42, and a speaker 44, all containedwithin a control module housing 46. The LCD 40 displays the operatingparameters of the electric water heater 10 such as the set pointtemperature (see bar graph 41 of FIG. 2), an energy savings level (e.g.,0, 1 or 2), and other useful information such as the date and time. Inaddition, the LCD 40 may be backlit to allow use of the control module12 in a dark or dimly-lit basement. The LEDs 42 are positioned adjacentto the LCD 40, but may also be incorporated into the LCD 40 to visuallyindicate operating parameters of the electric water heater 10. Thespeaker 44 allows the control module 12 to audibly alert a consumer of aparticular condition of the water heater 10. In addition to theforegoing, the control module 12 also includes at least user-inputdevice 48 (e.g., a button) to enable the consumer to communicate withthe consumer interface 45.

Turning to FIG. 3A, the control module 12 also comprises amicrocontroller 50 in communication with the sensor module 35 and theconsumer interface module 45. The microcontroller 50 is powered by apower supply 52 disposed generally within the control module housing 46.The power supply 52 receives power from line voltages L1, L2.

A limit control module 51 controls power to the heating elements 16, 18based on readings from the upper and lower temperature sensors 36, 38.The limit control module 51 of FIG. 3A is shown as an electronic limitcontrol module 53 and essentially acts as a backup device to themicrocontroller 50. For example, if the microcontroller 50 fails to cutpower to the upper and lower heating elements 16, 18, the electroniclimit control module 53 shuts down the heating elements 16, 18 based onreadings from the upper and lower temperature sensors 36, 38. The limitcontrol module 51 could also include a bimetal snap disc thermostat 55,as shown in FIG. 3B. The bimetal snap disc thermostat 55 receives linevoltages L1, L2 and selectively prevents power from reaching the upperand lower heating elements 16, 18.

In either of the foregoing configurations, the limit control module 51is a separate circuit from the microcontroller 50 and selectively cutspower to the upper and lower heating elements 16, 18 based on readingsfrom the upper and lower temperature sensors 36, 38. The limit controlmodule 51 only cuts power to the upper and lower heating elements 16, 18when the microcontroller 50 fails to do so based on readings from theupper and lower temperature sensors 36, 38.

The microcontroller 50 is also in communication with a sensorconditioning module 54 and a relay and driver module 56. The sensorconditioning module 54 receives the output from the respectivetemperature sensors 36, 38 and directs the output to the microcontroller50 and electronic limit control module 51. The relay and driver module56 receives event messages from the microcontroller 50 based on inputfrom the upper and lower temperature sensors 36, 38 to toggle the upperand lower heating elements 16, 18 between the ON state and the OFF stateby selectively allowing line voltage L1, L2 to supply current to therespective heating elements 16, 18.

Operation of the electric water heater 10 and associated control module12 is best understood with reference to FIGS. 4-7. Generally speaking,the control module 12 monitors the consumer's hot water usage over timeand provides an effective capacity for only the amount of hot water thatis actually needed. The control module 12 can reduce the effectivecapacity by reducing a consumer-selected selected set point temperatureby a setback value and recommend a reduction in the consumer-selectedset point temperature if further reductions to the set point temperatureare not possible. The control module 12 can increase the effectivecapacity by recommending an increase in set point temperature. In thismanner, the control module 12 is able to tailor the effective capacityof the water heater 10 to the actual hot water consumption of theconsumer.

When the water heater 10 is initially installed, the tank 14 iscompletely filled with cold water from the building water supply 24 viathe inlet 20. At this point, all of the water within the tank 14 issubstantially at the same temperature (i.e., cold). The consumer selectsa set point temperature setting at the consumer interface 45 bydepressing one of the buttons 48. The set point temperature representsthe temperature of the water that the control module 12 seeks to achievein the tank 14 within a tolerance. The tolerance recognizes that theactual water temperature within the tank may be different from themeasured temperature provided by sensors 36, 38. The set pointtemperature can be set, for example, to one of twenty temperaturesettings. The twenty settings are exemplified by the bar graph of FIG.2, though more or fewer temperature settings could be used. Therespective temperature settings provide the control module 12 adjuststhe effective capacity of the water heater 10.

In addition to selecting the desired set point temperature, the consumeris also able to select a desired energy savings setting, for example0—No Energy Savings, 1— Moderate Energy Savings, or 2— Aggressive EnergySavings. Selecting an energy level provides the control module 12 withthe ability to adjust the consumer set point temperature to tailoreffective capacity. The energy savings levels are exemplified by levels0, 1, 2 (FIG. 2) but could include additional energy savings levels. Theconsumer selects the respective energy savings setting at the consumerinterface 45 by depressing one of the buttons 48.

The first energy savings setting, 0—No Energy Savings, does not allowthe control module 12 to lower the consumer-selected set pointtemperature. The second energy savings level, 1—Moderate, allows thecontrol module 12 to lower the consumer-selected set point temperatureby an initial setback value. Thus, the temperature to which the water inthe water heater 10 will be heated is the control set point temperature,i.e., the consumer-selected set point temperature minus the initialsetback value. As already described, a lower water temperature in thetank 14 reduces the effective capacity of the electric water heater 10.At the reduced set point temperature, the consumer draws more hot waterfrom the tank 14 in order to obtain water at a desired temperature.Energy savings, though, is realized because the entire volume of waterin the tank 14 is heated to a lower temperature.

The third energy savings setting, 2—Aggressive, similarly allows theconsumer-selected set point temperature to be lowered by the initialsetback value. In addition, the second energy savings setting allows thecontrol module 12 to lower the set point temperature still further, byup to a maximum setback value. With the maximum setback value, thecontrol module 12 can further reduce the effective capacity of the waterheater 10 in an effort to optimize the energy efficiency of the waterheater 10 based on consumer demand for hot water.

Once the consumer selects a set point temperature and energy savingssetting, the control module 12 initially controls the water heater 10based on the respective consumer inputs (i.e., set point temperature andenergy savings setting).

In operation, the control module 12 first determines the control setpoint temperature based on the initial setback value. Note thatregardless of which energy savings level is selected (i.e., 1 or 2), thecontrol module 12 initially sets the control set point temperature to avalue equal to the consumer-selected set point temperature minus theinitial setback value, unless the energy savings level chosen is 0—NoEnergy Savings. In so doing, the control module 12 generates a controlset point temperature that is lower than the consumer-selected set pointtemperature, reducing the effective capacity of the water heater 10.With the control set point temperature determined, the control module 12then controls the function and operation of the electric water heater 10as previously described.

Once the water heater 10 is at the control set point temperature thecontrol module 12 monitors hot water consumption by the consumer. Bymonitoring the upper heating element 16, the control module 12 is ableto react to hot water usage and adjust effective capacity. As previouslydiscussed, the upper heating element 16 is only energized during a deepdraw event when the incoming cold water contacts the upper temperaturesensor 36. Therefore, the control module 12 is able to determine thatthe water heater 10 has excess effective capacity when the upper heatingelement 16 has not been energized for a predetermined period. Inaddition, the control module 12 is able to determine that there is aneed for additional effective capacity if the upper heating element 16has been energized for a predetermined period.

It should be noted that the predetermined amount of time is generallyreferred to as a “cycle” and is usually at least one week in duration toallow for a week's worth of household events that may give rise to adeep draw event such as, for example, laundry day. The control module 12may also collect usage data to generate historical usage data (i.e.,water usage over time). The control module 12 may then utilize thecollected historical data to develop usage patterns. The usage patternsmay be used by the control module 12 in anticipating setbacktemperatures for different times of day or days of the week. In thismanner, the control module 12 may control the capacity of the waterheater 10 based on historical information to prepare for certainhousehold events.

For example, if laundry day falls on Thursday for three consecutiveweeks, the control module 12 may increase the effective capacity of thewater heater 10 on Wednesday night in anticipation of laundry day.Conversely, if a consumer is routinely away from home on Saturdays andSundays, the water heater 12 may reduce the effective capacity on Fridaynight. Therefore, the control module 12 may be used to tailor energyconsumption based on consumer water usage and may collect data toanticipate future water usage.

If the control module 12 determines that there is excess effectivecapacity in the water heater 10, the control module 12 will take one oftwo actions. First, if the energy savings setting is set to level 1, thecontrol module 12 must continue to control the water heater at theconsumer-selected set point temperature minus the initial setback value.If conditions warrant a further decrease in effective capacity, however,the control module 12 alerts the consumer via consumer interface module45 to change the energy savings setting from level 1 to level 2. Second,if the energy savings setting is set to level 2, the control module 12lowers set point temperature by the maximum set back value to furtherreduce the effective capacity of the water heater 10. However, thecontrol module 12 is only permitted to reduce the set point temperatureby the maximum setback value.

Conversely, if the control module 12 determines that there is not enougheffective capacity in the water heater 10, the control module 12increases the effective capacity by raising the control set pointtemperature, but is limited in doing so by the consumer-selected setpoint temperature.

FIG. 4 details an exemplary savings module 58 for use by the controlmodule 12 for determining when an increase or a decrease in effectivecapacity is warranted. The energy savings module 58 utilizes the controlmodule 12 and associated sensor module 35 to tailor the effectivecapacity of the water heater 10 to the specific needs of the individualconsumer by continuously monitoring the consumer's hot water usage.Initially, the control module 12 compares the consumer-selected setpoint temperature to a threshold cutoff temperature, which is too low toallow operation of the energy savings module 58 (i.e., a setback fromthe consumer-selected set point temperature would result in a cold watercondition). In one exemplary embodiment, the cutoff temperature isbetween 115 degrees Fahrenheit and 120 degrees Fahrenheit. Thereforewhen the consumer-selected set point temperature is lower than thecutoff temperature (i.e., 115-120 degrees Fahrenheit), the energysavings module 58 sets the control set point temperature at theconsumer-selected set point temperature at 62 as the control module 12cannot setback the temperature lower than 115 degrees Fahrenheit. Atthis point, the control module 12 maintains the water disposed withinthe tank 14 at the consumer-selected set point temperature byselectively toggling the upper and lower heating elements 16, 18 betweenthe ON and OFF states.

If the consumer-selected set point temperature is above the cutofftemperature, the control module 12 reduces the consumer-selected setpoint temperature by the initial setback amount to the control set pointtemperature at 64. Once the control set point temperature is determined,the control module 12 maintains the water within the tank 14 at thecontrol set point temperature by selectively toggling the upper andlower heating elements 16, 18 between the ON and OFF states.

The control module 12 controls the water heater 10 at the control setpoint temperature for one cycle (i.e., at least one week). The controlmodule 12 monitors the sensor module 35 to determine if the upperheating element 16 has been energized during the cycle at 66. If theupper heating element 16 has been energized during the cycle, thecontrol module 12 concludes that the water heater 10 has experienced adeep draw event and requires additional effective capacity at 68.However, if the upper element 16 has not been energized during thecycle, the control module 12 references a timer to determine whether thecycle has expired at 70. If the timer has expired (indicating that thecycle has ended), the control module 12 concludes that the water heater10 has not experienced a deep draw event within the last cycle at 72. Atthis point, the control module 12 concludes that the set pointtemperature should be further reduced to decrease the effective capacityof the water heater 10.

The control module 12 determines a float range for the setback valuebased on whether the upper heating element 16 has been energized duringthe last cycle at 74. The float range defines an amount the controlmodule 12 is allowed to either increase or decrease the set pointtemperature to effectuate a change in effective capacity. The controlmodule 12 is limited in implementing the float range by the maximumsetback value as the control module 12 is not permitted to reduce theconsumer-selected set point temperature more than the maximum setbackvalue at 76. In addition, the control module 12 is limited by the cutofftemperature (i.e., 115-120 degrees Fahrenheit).

If the control module 12 determines that additional energy savings arepossible because the upper heating element 16 has not cycled for apredetermined time, or that the water heater 10 is not producing enoughhot water to keep up with demand (i.e., the upper heating element 16 isregularly cycled ON), the control module 12 alerts the consumer. Thecontrol module 12 notifies the consumer that at least one of the setpoint temperature setting or the energy savings level should be adjustedto allow the control module 12 the flexibility to optimize performanceof the water heater 10. The control module 12 recommends such actionthrough use of a performance monitoring module 78 to rectify an overcapacity or an under capacity situation.

With particular reference to FIG. 5, operation of the performancemonitoring module 78 is described. The performance monitoring module 78generates a recommendation to the consumer to save energy by selecting alower set point temperature or generates a recommendation to theconsumer to increase the set point temperature based on hot water demandhistory. For example, if the setback value is equal to the maximumsetback value, the control module 12 cannot further reduce theconsumer-selected set point temperature even if there is excesseffective capacity in the water heater 10. Therefore, the only way forthe control module 12 to reduce the effective capacity of the waterheater 10 is to start at a lower consumer-selected set pointtemperature. Therefore, the control module 12 must alert the consumerthat the consumer-selected set point temperature should be adjusted.

The control module 12 first determines if the setback value equals themaximum setback value at 80. If the setback value equals the maximumsetback value, and the upper heating element 16 has not cycled ON for apredetermined period of time, the control module 12 recommends to theconsumer via the LCD 40, LED 42, and/or speaker 44 that theconsumer-selected set point temperature should be reduced to realizefurther energy savings at 82. If the consumer reduces the set pointtemperature, the control module 12 is able to further reduce theeffective capacity of the water heater 10 by calculating the control setpoint temperature from a lower consumer-selected set point temperature.Such a reduction in effective capacity ultimately saves the consumerenergy as excess water is not needlessly heated. In this manner, eventhough the control module is restricted from reducing theconsumer-selected set point temperature by the maximum setback value,the control module 12 can still further reduce the effective capacity ofthe water heater 10.

If the setback amount is zero, and the upper heating element 16 has beencycled ON during a previous period, the control module 12 determinesthat an increase in effective capacity is necessary at 84. At thispoint, the control module 12 alerts the consumer of the need foradditional effective capacity at 86 and recommends increasing theconsumer-selected set point temperature via the LCD 40, LED 42, and/orspeaker 44. If the control module 12 is able to properly control theeffective capacity of the water heater 10 based on hot water demand andconsumer-selected input, the control module 12 displays that the systemis functioning within its limits and is able to sufficiently optimizethe effective capacity of the water heater 10 at 88.

In each of the foregoing situations, the control module 12 must alertthe consumer to either raise or lower the consumer-selected set point ifthe maximum setback is achieved. The control module 12 makes suchrecommendations through a consumer interface display module 90.

The consumer interface display module 90 for use with theabove-described performance monitoring module 78 is shown in FIG. 6. Theconsumer interface display module 90 determines whether the LCD 40recommends an increase in the consumer-selected set point temperatureand whether the consumer has acted on the recommendation 92. If theconsumer has acted on the recommendation, the recommendation is removedand the display 40 notes that the system is functioning within limits.At this point, the control module 12 sets the setback value to begenerally equal to the initial setback value plus the amount that theconsumer-selected set point temperature was increased 96.

Similarly, the consumer interface display module 90 determines whetherthe LCD 40 recommends a decrease in the consumer-selected set pointtemperature and whether the consumer has acted on the recommendation 98.If the consumer has acted on the recommendation, the recommendation isremoved and the display 40 that the system is functioning within limitsand is able to sufficiently optimize the effective capacity of the waterheater 10 at 100. At this point, the control module 12 sets the setbackvalue to be generally equal to the initial setback value minus theamount that the consumer-selected set point temperature was decreased102.

It should be noted that for the consumer interface display module 90,the consumer's acting on the recommendation (i.e., to raise or lower theset point temperature range) does not immediately change the temperatureof the water disposed within the tank 14. Following the recommendationsimply shifts the control module's 12 operational limits so that thecontrol module 12 has greater flexibility to further adjust theeffective capacity of the water heater 10 when necessary in view of hotwater demand history, thereby realizing greater energy efficiency.

The control module 12, by optimizing effective capacity of the waterheater 10, allows more hot water to be available at lower set pointtemperatures, as demonstrated by the differential module 104 of FIG. 7.

During periods of non-use, the temperature of water within the tank 14will fall due to heat escaping through tank walls. Therefore,maintaining the tank 14 at a lower temperature reduces energy loss. Atlower set point temperatures, the water within the tank 14 is onlyallowed to vary from the set point temperature a small amount toincrease the average temperature of the tank 14. Reducing the operatingrange of the tank 14 at lower set point temperatures ensures that thereis enough hot water within the tank 14 to deliver water at a comfortabletemperature (i.e., the delivered temperature).

For higher set point temperatures, the differential module 104 allows awider temperature differential (i.e., 12° F.) between the set pointtemperature and the temperature of the water at which the heatingelements 16, 18 are energized. For lower temperatures, the differentialmodule 104 allows a narrower temperature differential (i.e., 7° F.).This relationship allows more hot water to be available at lower setpoint temperatures. For example, a set point temperature of 145° F.requires a differential of 12° F., thereby allowing the water to rangebetween 133° F. and 157° F. A set point temperature of 105° F. requiresa differential of 7° F., thereby allowing the water to range between 98°F. and 112° F.

Each degree lost by the water heater 10 during non-use has a greaterimpact in reducing effective capacity at lower set point temperaturesthan at higher set point temperatures. Maintaining the temperature ofthe water close to the set point temperature allows more hot water to beavailable.

Therefore, by controlling the effective capacity of the water heater 10to a state that minimizes the set point temperature (i.e., by reducingthe consumer-selected set point temperature by the setback value), morehot water is available at lower set point temperatures and energy issaved.

FIG. 8 schematically represents the relationship between the controlmodule 12, sensor module 35, energy savings module 58, performancemonitoring module 78, user interface module 90, and differential module104. Each of the modules 35, 58, 78, 90, 104 communicate with thecontrol module 12 to aid the control module 12 in continuously adjustingthe set point temperature of the water heater 10 until the effectivecapacity and energy use are optimized.

The description of the invention is merely exemplary in nature and,thus, variations that do not depart from the gist of the invention areintended to be within the scope of the invention. Such variations arenot to be regarded as a departure from the spirit and scope of theinvention.

1. An electric water heater comprising: a tank defining a volume; awater inlet fluidly coupled to said tank; a water outlet fluidly coupledto said tank; at first heating element extending into said tank anddisposed proximate to said inlet; a second heating element extendinginto said tank and disposed proximate to said outlet; and a controlmodule operable to control the effective capacity of the water heater byselectively toggling one of said first and second heating elementsbetween an ON state and an OFF state to heat water disposed within saidtank to a control temperature, said control module determining saidcontrol temperature based on the actuation of said second heatingelement.
 2. The electric water heater of claim 1, wherein said controltemperature is less than a consumer-selected set point temperature by asetback value.
 3. The electric water heater of claim 2, wherein saidsetback value is determined by said control module and is based on aconsumer-selected energy savings setting.
 4. The electric water heaterof claim 1, wherein said control module includes a consumer interfacemodule.
 5. The electric water heater of claim 4, wherein said consumerinterface module includes a visual display.
 6. The electric water heaterof claim 5, wherein said visual display includes at least one of alight-emitting device and a liquid crystal display.
 7. The electricwater heater of claim 1, further comprising a sensor module incommunication with said control module.
 8. The electric water heater ofclaim 7, wherein said sensor module includes at least one flow sensor.9. The electric water heater of claim 7, wherein said sensor moduleincludes at least one temperature sensor associated with each of saidfirst and second heating elements.
 10. The electric water heater ofclaim 1, wherein said control temperature is modified from a set pointtemperature by a setback value to control an effective capacity of theelectric water heater.
 11. A control system for an electric water heaterhaving an upper heating element and a lower heating element, the controlsystem comprising: a control module that controls operation of theelectric water heater by selectively toggling the upper and lowerheating elements between an ON state and an OFF state; and a consumerinterface module that allows a consumer to input a set point temperaturefor the electric water heater; wherein said control module continuouslymonitors and adjusts said set point temperature by a predetermined valueuntil an optimum effective capacity of the water heater is achieved. 12.The control system of claim 11, wherein said predetermined value isdictated by said consumer interface module and is a function of aconsumer-selected energy savings setting.
 13. The control system ofclaim 11, wherein said consumer interface module includes a visualdisplay.
 14. The control system of claim 13, wherein said visual displayincludes at least one of a light-emitting device and a liquid crystaldisplay.
 15. The control system of claim 11, further comprising a sensormodule, said sensor module receiving output from at least one sensor forinput into said control module.
 16. The control system of claim 11,further comprising at least one sensor in communication with saidcontrol module.
 17. The electric water heater of claim 16, wherein saidat least one sensor is a temperature sensor.
 18. The electric waterheater of claim 16, wherein said at least one sensor is a flow sensor.19. The electric water heater of claim 11, wherein said control moduledetermines said optimum effective capacity based on the frequency saidupper heating element is toggled into said ON state.
 20. A controlsystem for an electric water heater having an upper heating element anda lower heating element, the control system comprising: a control modulethat controls operation of the electric water heater by selectivelytoggling the upper and lower heating elements between an ON state and anOFF state; and a consumer interface module that allows a consumer toinput a set point temperature for the electric water heater; whereinsaid control module adjusts said temperature by a predetermined value tooptimize an effective capacity of the water heater; wherein saidconsumer interface recommends an adjustment to said set pointtemperature when said predetermined value is achieved and the upperheating element has remained in said OFF state for a predeterminedperiod.
 21. The control system of claim 20, wherein said consumerinterface recommends an increase in said set point temperature when theupper heating element is toggled into said ON state to thereby increasethe effective capacity of the water heater.
 22. The control system ofclaim 20, wherein said predetermined value includes a first value and asecond value, said first value and said second value being fixed,regardless of said set point temperature.
 23. The control system ofclaim 22, wherein said consumer interface module includes an energysavings setting allowing a consumer to choose said predetermined valueto either said first value or to said second value.
 24. A method forcontrolling an electric water heater comprising: filling the waterheater with water; setting a set point temperature; reducing said setpoint temperature to a first control temperature, said first controltemperature being less than said set point temperature by a firstsetback value; energizing one of upper and lower heating elements untilsaid water achieves said control temperature; monitoring said watertemperature with an upper temperature sensor and a lower temperaturesensor; supplying current to one of said upper and lower heatingelements when said water temperature falls below said first controltemperature; reducing said set point temperature to a second controltemperature if said upper heating element is not energized for apredetermined amount of time, said second control temperature being lessthan said set point temperature by a maximum setback value.
 25. Thecontrol method of claim 24, further comprising recommending a reductionin set point temperature if said upper heating element is not energizedfor a predetermined amount of time and said set point temperature hasbeen reduced to by said maximum setback value.
 26. The control method ofclaim 24, further comprising recommending an increase in set pointtemperature if said upper heating element is energized a predeterminednumber of times over a predetermined time period and said water is atsaid first control temperature.
 27. The control method of claim 24,further comprising generating an alert message if said second controltemperature is achieved and said upper heating element has not beenenergized for a predetermined amount of time.
 28. The control method ofclaim 27, wherein generating said alert message includes at least one ofa visual indication and an audible alarm.
 29. A method for controllingan electric water heater comprising: filling the water heater withwater; selecting a set point temperature; selecting an energy savingssetting at one of a plurality of energy savings settings; reducing saidset point temperature to a first control temperature, said first controltemperature being less than said set point temperature by an initialsetback value corresponding to said first energy savings setting;energizing one of upper and lower heating elements until said waterachieves said control temperature; monitoring said water temperaturewith an upper temperature sensor and a lower temperature sensor;supplying current to one of said upper and lower heating elements whensaid water temperature falls below said first control temperature;reducing said set point temperature to a second control temperature ifsaid upper heating element is not energized for a predetermined amountof time and said second energy savings setting is selected, said secondcontrol temperature being less than said set point temperature by amaximum setback value.
 30. The control method of claim 29, furthercomprising recommending a reduction in set point temperature if saidupper heating element is not energized for a predetermined amount oftime and said set point temperature has been reduced by said maximumsetback value.
 31. The control method of claim 29, further comprisingrecommending an increase in set point temperature if said upper heatingelement is energized a predetermined number of times over apredetermined time period and said water is at said first controltemperature.
 32. The control method of claim 29, further comprisinggenerating an alert message if said second control temperature isachieved and said upper heating element has not been energized for apredetermined amount of time.
 33. The control method of claim 32,wherein generating said alert message includes at least one of a visualindication and an audible alarm.